Age of Xingfuzhilu Formation and Contact Relationship between Permian and Triassic strata in southern Da Hinggan Mountains: Constraints from the tuff zircon U-Pb ages

Abstract: The final suture position between North China plate and Siberia plate remains a topic of much controversy. Lots of researchers prefer describing West Lamulun River - Changchun - Yanji fault as the final suture zone of the two plates, but dispute still exists concerning the final closure time. One of the reasons is that there exists controversy concerning the Late Permian－Early Triassic stratigraphy in the Da Hinggan Mountains due to insufficient research; in particular, the study of the contact relationship between Late Permian and Lower Triassic remains very insufficient. The Early Triassic Xingfuzhilu Formation is of fluvial-lacustrine facies with red bed features and contains fossils such as ostracoda, sporopollen, conchostracan, bivalves and megaplants, which are located in southern Da Hinggan Mountains. The authors collected tuff samples and made analysis. LA-ICP-MS U-Pb dating of zircon yielded an age of (254.3±2.6) Ma. Combined with the existing volcanic dating and fossils in the upper part of the volcanic rocks, it is considered that the lower part of the third member of Xingfuzhilu Formation should be of Late Permian whereas the upper part belongs to Early Triassic, and that the Late Permian-Early Triassic strata are of continuous deposition. The Paleo-Asian Ocean experienced collision suturing and the biota mixture in late Late Permian, and the closing time of the two plates should be Early Triassic.